Search engine marketing, or SEM, is a form of Internet marketing that seeks to promote websites by increasing their visibility in search engine result pages (SERPs) through the use of paid placement, contextual advertising, and paid inclusion. The industry peak body Search Engine Marketing Professional Organization (SEMPO), includes search engine optimization (SEO) within its reporting, and SEO is also included in the industry definitions of SEM by Forrester Research, eMarketer, Search Engine Watch, and industry expert Danny Sullivan. The New York Times defines SEM as 'the practice of buying paid search listings
In 2006, North American advertisers spent US$9.4 billion on search engine marketing, a 62% increase over the prior year and a 750% increase over the 2002 year. The largest SEM vendors are Google AdWords, Yahoo! Search Marketing and Microsoft adCenter. As of 2006, SEM was growing much faster than traditional advertising and even other channels of online marketing. Because of the complex technology, a secondary "search marketing agency" market has evolved. Many marketers have difficulty understanding search engine marketing and they rely on third party agencies to manage their search marketing.